It is becoming clear that epigenetic changes are involved in cancer as much as in normal development. We recently identified RBP2, a protein interacting with the pRB tumor suppressor, which seems to mediate the pRB function in differentiation. RBP2 and the closely related protein PLU1 are two newly identified histone demethylases associated with malignancy. Their transcriptional regulation has been connected to the demethylation of trimethylated lysine 4 of histone H3 (H3K4me3). We recently identified differentiation- specific RBP2 targets genome-wide. We propose that RBP2 establishes, in a pRB dependent manner, a transcriptional program that regulates progression to a more differentiated state and may be a requisite component of leukemia and lymphoma development. In this application we will study how RBP2 is recruited to its genomic targets and which factors change the affinity or specificity of RBP2 binding. We suggest to use molecular, cell biological and genetic approaches to fulfill the following specific aims: (1) To determine the requirements of histone H3K4 methylation, sequence-specific DNA binding, the three PHD finger cassettes and E2F binding for RBP2 recruitment to genomic loci; (2) To dissect the RBP2 recruitment mechanisms that result in gene expression changes; (3) To determine RBP2 target gene expression in cancer cells deficient in RBP2 function compared with normal cells. This study will contribute to the development of therapeutic approaches involving this novel class of epigenetic regulators.